Thermal insulation device for a very low-temperature line

ABSTRACT

Thermal insulation device for a very low-temperature line comprising a thermal screen around the line, a pulverulent insulating material and an outer casing surrounding the whole device. The thermal screen consists of two half-shells made of an invariable alloy and assembled longitudinally by means of thermally and electrically insulating spacers so as to enable the degassing of the pulverulent insulating material from the inside of the screen.

United States Patent [1 1 Aupoix et al.

[451 Dec. 18, 1973 1 1 THERMAL INSULATION DEVICE FOR A VERY LOW-TEMPERATURE LINE [76] inventors: Marcel Aupoix, 10 rue Maublanc,

Paris, France 75015; Francois Muisson-Franckhauser, 94 Blvd. de France, Brettigny-sur-Orge, France 91220; Jean-Marie Leroux, 5 rue Eugene Delacroix, Grenoble; Roger Prost, Domaine Saint-Hugues, Saint-Egreve, both of France 38 22 Filed: Aug. 23, 1972 21 Appl. No.: 283,133

[30] Foreign Application Priority Data Aug. 23, 1971 France 7130534 [52] US. Cl 174/15 C, 174/27, l74/DlG. 6 [51] Int. Cl HOlv 11/00 [58] Field of Search 174/15 R, 15 C, 16 B,

174/27, 68 C, 99 B, DIG. 6; 335/216 [56] References Cited UNITED STATES PATENTS 3,693,648 9/1972 Sassin 174/15 C 3,600,498 8/1971 Aupoix ct a1. 174/15 C 3,595,982 7/1971 3,343,035 9/1967 Garwin 174/15 C Primary Examiner-Bernard A. Gilheany Assistant Examiner-A. T. Grimley AttorneyRichard C. Sughrue et al.

[ 5 7] ABSTRACT 8 Claims, 4 Drawing Figures 'snmaur 3 FIG. 2

PATENTH] DEC I 8 I973 sum 3 or 3 FIG.4

THERMAL INSULATION DEVICE FOR A VERY LOW-TEMPERATURE LINE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal insulation device for a very low temperature line.

2. Prior Art It is known in the prior art to thermally insulate a line consisting of one or more very low temperature channels by means of a device comprising:

a metal thermal screen surrounding this line. The line itself is provided with cooling conduits in which a cryogenic fluid circulates;

an outer metal case about this screen;

wires for suspending the line in the screen and the screen in the outer case.

A vacuum is generally created between the line and the outer case and a thermal insulation device occupies the space between the screen and the outer case.

A disadvantage of this thermal insulation device is the longitudinal displacement of the low temperature line with respect to the outer case at ambient temperature. In fact, the cooling of channels to be thermally insulated causes thermal contraction of the same.

The structure of a thermal insulation device of the type described above is not adapted to respond sufficiently well to the conditions of thermal insulation and the circulation of cooling fluids. Furthermore, it is complicated to produce and thus costly and the stress problems resulting from the temperature are difficult to resolve.

SUMMARY OF TI-IE INVENTION outer case conduits for cooling the screen, intermediate parts for mechanically assembling the parts of the screen while thermally insulating them from each other, characterized in that the parts of the screen consist of a materiahthe relative thermal contraction of which is less than 5.10".

A device according to the invention for the thennal insulation of very low temperature channels will now be described withreference to the accompanying three diagrammatic figures provided by way of non-limitative examples. In the embodiment, which will be described with reference to these figures, the very lowtemperature channel consists of the inner case of a superconductive cryogenic line. In the drawings:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I shows a sectional view in perspective of a first embodiment of a device according to the invention.

FIG. 2 shows a sectional view in perspective of a second embodiment of a device according to the invention.

FIG. 3 shows an axial sectional view in perspective of a section of the device according to FIGS. 1 or 2 comprising a barrier which is rendered air and water tight by the inner and outer cases.

FIG. 4 shows an axial sectional view of a section of a device according to FIGS. 1 and 2 provided with connection means for a pump.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The cryogenic line shown in perspective as a diagrammatic section in FIG. 1 comprises:

an inner tubular-shaped case 2 containing a line consisting of hollow electric cables such as the cable 4. The number of these cables has been limited to four when a powerful current, for example,a continuous current is being conveyed but it is obvious that this number may be varied. A cooling fluid which may, for example, be liquid helium, circulates about these cables in the case 2 as well as in the inner part 6 of the cables. These cables are constructed in a known way so as to render their length invariable in respect of the temperature.

Cooling fluid return conduits 8 and 10 in the inner case, are separated from this case by the thermally insulating wedges 44,46 and 48 as shown in the figure.

These conduits consist of an invariable alloy, i.e., the relative thermal contraction of which is lower than 5.10. (The coefficient of thermal contraction representing the linear contraction per unit length, the temperature passing from the ambiant temperature to the operating temperature). This alloy may consist of iron and nickel with a 30 -45 percent nickel concentration. It may, for example, be a type of alloy known under the mark INVAR CRYOGENIQUE sold in France by the metallurgical company IMPHY.

With conduits consisting of an alloy having low thermal contraction and an inner case with low thermal contraction it is possible to obtain a cryogenic line, the central so-called cold part of which is of invariable length.

A thermal screen in the form of a cylinder consists of two shells, the upper one designated by 12 and the lower one 14. These two shells combine along two generatrices of this cylinder.They are made of an invariable alloy which may be the same as that of the conduits 8 and 10.

Intermediate assembly parts for the two shells consist of thermally insulating spacers such as 16 and 18 regularly distributed along the length of the thermal screen. The shape of these spacers has been adapted to that of the half-shells to permit the longitudinal assembly of the latter. These insulating spacers allow wires such as 38 to be mounted to support the inner case in the screen. These wires also support the conduits 8 and 10 and keep them in contact with the inner case.

The conduits 20, 22, 24, 26, consist of the same invariable alloy. These conduits allow the screen to be cooled by means of a cryogenic fluid, for example, nitrogen.The lower conduits 22 and 24 ensure the circulation of the fluid in one direction and the conduits 20 and 26 ensure the return of this fluid in the other direction. These conduits are soldered to the screen so as to be in good thermal contact with the same.

An outer case 28, is made of steel, for example,and closed by a soldering joint 32. A receiver cradle 34 is provided to receive a wire 36 for suspending the screen and its contents in this outer container.

A thermal insulator 42 consisting of pulverulent alumina, .for example, occupies the space between the thermal screen and the outer case. The spacers 16 and 18 are interrupted, the gaps between these spacers providing the openings 51. At the level of these spacers the thermal screen is covered with a band of felt 50. This permits the pumping of the area between the inner and outer cases while preventing the penetration of the powder into the space between the thermal screen and the inner case.

It is obvious that the thermal insulation is augmented by the creation of a vacuum in the space between the inner case 2 and the outer case 28. This vacuum is maintained by the cryopumping which results from the presence of the very low-temperature inner case 2.

FIG. 2 is a diagrammatic sectional view in perspective of another embodiment of a cryogenic line according to the invention.

This cryogenic line which is intended for conveying high electrical intensities in alternating current, for example, comprises:

an inner tubular-shaped case 220, made of an invariable alloy and containing hollow cables of invariable length such as the cable 60. In the case of an alternating current these cables are in the form of conductive layers consisting of flat conductors disposed in helical lines and an insulating band provided between these coaxial layers.

In the case of the embodiment selected for conveying alternating current the number of conductors was limited to three but it is obvious that this number may be varied. A cooling fluid, which may be liquid helium circulates about these cables in the case 220 as well as inside the same.

The inner case 220 is rendered air and water tight by means of a soldered joint 690.

A conduit 80 returns the cooling fluid in the inner case, said conduit being separated from the case by a thermally insulating trim strip 600, wound in a helical line about the conduit 80.

With this conduit consisting of an invariable alloy together with the inner case 22 consisting of an invariable alloy it is possible to obtain a cryogenic line, the socalled "cold" part of which is of invariable length.

A thermal screen in the form of a cylinder is composed of two halt shells, the upper one being designated by 120 and the lower one by 140. These two half shells are combined along two generatrices of this cylinder and consist of an invariable alloy.

Intermediate parts 180 for the assembly of the two shells are thermally insulating and their shape is adapted to conform to that of the half shells and thus permits the longitudinal assembly of the same.

Mechanical reinforcement arches 550,560 are attached to the inner face of each half shell. They are regularly distributed along the screen andare made, for example, of aluminum. The arches according to this embodiment permit the suspension means or wires 380 for the inner case 220 to be hung up in the lower half shell 140 of the screen. They also increase the thermal conductance of the screen thus providing greater uniformity of temperature. The cooling fluid liquid helium) return conduit 80 for the inner case may be kept in place by means of the collar 610 fitted with the tightening buckle 620.

Means circulate a cooling fluid (liquid azote or nitrogen) about the screen. These are represented in the figure by the conduits 240 and 260. The conduit 240 in thermal contact with the lower shell 140 of the screen enables the cooling fluid to circulate in the outward" direction and the conduit 260 in thermal contact with the upper shell 120 allows this fluid to flow in the return direction. These conduits are made of an invariable alloy and are soldered to the screen.

An outer steel case 280, rendered air and water tight by the longitudinal soldered joint 630,surrounds the thermal screen. The suspension means 640,650 for suspending the screen in the outer case are attached to this case at 660.

Two tightening collars 670,680 enable the two half shells to be kept opposite each other.

A thermal insulator 420 consisting of pulverulent aluminum occupies the space between the screen and the outer case 280. A felt band 500 which permits the cryopumping of the space between the inner and outer case while preventing the insulating powder from penetrating between the thermal screen and the inner case is disposed at the intermediate parts 180.

The advantages of the cryogenic line according to the invention described with reference to the accompanying diagrammatic FIGS. 1 and 2 result principally from the invariability of the length of the screen and its cooling conduits. In fact, this invariability of the length of the screen is obtained by anchoring the thermal screen with respect to the outer case 28 or 280. The provision of anchoring means at the two ends of a rectilinear section creates longitudinal traction stresses in the thermal screen which areequal to the product of the elasticity modulus of the alloy constituting the thermal screen by the free relative thermal contraction of this alloy. These stresses remain ca. 6kg/mm2. A cryogenic line according to the invention is thus made up of sections a few hundred meters in length with slight curves between successive anchoring points to reduce the reactions at the supports 36 or 640 and 650.

According to FIG. 3 the anchor ties of the two shells 12,14 securing the thermal screen with respect to the outer case 28 or 280 consist advantageously of barriers such as 111 attached to the inner case 2 and outer case 28 and disposed so as to render the space between two successive barriers air and water tight. The outer case and the inner case of invariable length are made of material having similar properties to that used for the thermal screen.

The cryogenic line constituted in this way is characterized in that the barriers acting as anchoring ties eliminate both the thermal contraction of the screen and that of the elements at the temperature of the cryogen cable or the very low temperature line.

FIG. 4 shows the inner case 2, the two parts 12 and 14 of the screen and the outer case 28 of the cryogenic line of FIG. 1. FIG. 4 also shows a radial conduit 101 bringing into communication the space inside the two parts 12 and 14 of the screen with the space outside the outer container 28. This conduit also permits the connection by way of the pipe 103 of pumping means (not shown). These pumping means may have a very high capacity when the cryogenic line is first put under a vacuum and may subsequently have a very low capacity to pump the cryogenic gas leaks which cannot be cryopumped.

The invention is obviously not limited to the embodiments which have been described and represented by way of example only. More particularly, without departing from the scope of the invention certain dispositions and certain means may be replaced by equivalent means.

Thus the thermal insulation device for a very low temperature line according to the invention may be used in particular in the following cases:

the line is a channel or a number of channels for conveying cryogenic fluids or liquified gas;

the line is a cryogenic line for the transmission of high electrical intensities in continuous or alternating current;

the line comprises coaxial superconductor cables for conveying information.

We claim:

1. In a thermal insulation device for a very lowtemperature line and comprising; a thermal screen in the form of a metal cylinder surrounding said line, said screen consisting of at least two parts assembled along two generatrices of the formed cylinder, an outer water and air tight cylindrical, metal case surrounding said screen, a thermally insulating powder occupying the space between the screen and the outer case, means for suspending the line in the screen and means for suspending the screen in the outer case, at least one intermediate part disposed along each of said generatrices for the mechanical assembly of the parts of said screen while insulating them thermally from each other, the two parts of said screen each bearing in good thermal contact at least one cooling conduit, means for circulating a cooling fluid in a forward direction in the cooling conduit borne by one of the parts and in a return direction in the cooling circuit borne by the other part, the improvement wherein:

means including said intermediate parts define openings to allow communication between the space inside and outside the screen without permitting the passage of the powder therethrough but allowing the degassing of the powder from the inside of the screen.

2. The device according to claim 1, wherein said means defining openings comprises said plurality of intermediate parts being aligned along each of the generatrices with gaps between these parts and said means preventing the passage of powder through said openings comprising a permeable band having a fibrous structure secured along each of the generatrices on the outer face of said parts and sealing said gaps.

3. The device according to claim 1, wherein said improvement further comprises: the means for suspending the line in the screen being fastened to the intermediate parts.

4. The device according to claim 1, wherein said improvement further comprises: each of the parts of the screen including mechanical reinforcement means consisting of metal arches attached to the parts of the screen and distributed along the screen.

5. A device according to claim 4, wherein: the arches are made of aluminum.

6. A device according to claim 4, wherein: the means for suspending the line in the screen are fastened to the arches.

7. The device according to claim 1, wherein said improvement further comprises: the anchor ties securing the thermal screen with respect to the outer case being disposed at intervals axially of said device.

8. A device according to claim 7, wherein: the anchor ties seal, in a fluid tight manner, the space between the outer case and the line. 

1. In a thermal insulation device for a very low-temperature line and comprising; a thermal screen in the form of a metal cylinder surrounding said line, said screen consisting of at least two parts assembled along two generatrices of the formed cylinder, an outer water and air tight cylindrical, metal case surrounding said screen, a thermally insulating powder occupying the space between the screen and the outer case, means for suspending the line in the screen and means for suspending the screen in the outer case, at least one intermediate part disposed along each of said generatrices for the mechanical assembly of the parts of said screen while insulating them thermally from each other, the two parts of said screen each bearing in good thermal contact at least one cooling conduit, means for circulating a cooling fluid in a forward direction in the cooling conduit borne by one of the parts and in a return directioN in the cooling circuit borne by the other part, the improvement wherein: means including said intermediate parts define openings to allow communication between the space inside and outside the screen without permitting the passage of the powder therethrough but allowing the degassing of the powder from the inside of the screen.
 2. The device according to claim 1, wherein said means defining openings comprises said plurality of intermediate parts being aligned along each of the generatrices with gaps between these parts and said means preventing the passage of powder through said openings comprising a permeable band having a fibrous structure secured along each of the generatrices on the outer face of said parts and sealing said gaps.
 3. The device according to claim 1, wherein said improvement further comprises: the means for suspending the line in the screen being fastened to the intermediate parts.
 4. The device according to claim 1, wherein said improvement further comprises: each of the parts of the screen including mechanical reinforcement means consisting of metal arches attached to the parts of the screen and distributed along the screen.
 5. A device according to claim 4, wherein: the arches are made of aluminum.
 6. A device according to claim 4, wherein: the means for suspending the line in the screen are fastened to the arches.
 7. The device according to claim 1, wherein said improvement further comprises: the anchor ties securing the thermal screen with respect to the outer case being disposed at intervals axially of said device.
 8. A device according to claim 7, wherein: the anchor ties seal, in a fluid tight manner, the space between the outer case and the line. 